A semiconductor device manufacturing process includes a step for performing a plasma process such as an etching process, a film forming process or the like on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) as a substrate by using a plasma.
For example, an etching process is performed on multilayer films having different compositions, e.g., a bottom anti-reflection coating film, an amorphous carbon film, a silicon oxide film, an etching stop film and the like, which are laminated below a pattern mask in that order from the top on an silicon film of a pattern mask. Therefore, when a recess is formed in these multilayer films, an etching gas is changed for each film and, also, processing conditions such as a flow rate of the etching gas, a pressure and the like are controlled for each film. In order to uniformly etch each of the films, it is required to supply a processing gas such that the concentration thereof becomes uniform in a processing region above a wafer in accordance with the processing conditions for each film and to convert the processing gas into a plasma uniformly.
As for a method for performing a plasma process by using a plasma of a processing gas, there have been known, e.g., a CCP (capacitively coupled plasma) processing method, an ICP (inductively coupled plasma) processing method, a method using microwaves and the like.
The CCP processing method uses a parallel plate type plasma processing apparatus in which a processing gas supplied from a gas shower head formed of, e.g., a metal, and having at a bottom portion thereof a plurality of gas injection openings is converted into a plasma by applying a high frequency voltage between the gas shower head and a mounting table which mounts thereon a wafer in a processing chamber, the gas shower head being provided at a ceiling wall of the processing chamber so as to face the wafer. In this method, the processing gas is supplied from the shower head, so that the concentration distribution thereof in the processing region can be controlled even when the processing conditions such as the flow rate and the type of the processing gas are changed. Due to the uniform distribution of the concentration of the processing gas and the close installation of the mounting table and the gas shower head, the height of the processing chamber can be reduced. Moreover, the gas shower head is formed of an easily processable material, e.g., a metal, so that a cooling mechanism, e.g., a cooling water path, can be simply provided at the gas shower head. Accordingly, the temperature of the gas shower head can be easily controlled in accordance with the processing conditions.
However, in the CCP processing method, a path of a current flowing between the mounting table and the gas shower head is extremely complicated. Thus, it is difficult to uniformly convert the processing gas into the plasma, and the plasma density on the surface of the wafer is apt to be non-uniform. Accordingly, an etching rate in a diametrical direction of the wafer, for example, may be varied. Further, in this method, a high electron temperature of the plasma may inflict damages on the wafer. Moreover, a high frequency power supply needs to be connected to both or one of the mounting table and the gas shower head and, hence, the cost of the apparatus is increased.
The ICP processing method that has been conventionally used utilizes electromagnetic induction as described in, e.g., Japanese Patent Application Publication No. 2008-109155 (FIG. 1). Specifically, an ICP coil wound multiple times coaxially with respect to a wafer is provided at the ceiling wall of the processing chamber which is formed of a dielectric material, e.g., quartz. By applying a high frequency voltage to the coil, an electric field is generated in the processing chamber through the ceiling wall. The processing gas is turned into a plasma by the electric field thus generated. In this method, the electric field is generated below the coil, and the intensity of the electric field is changed in accordance with the value of the voltage applied to the coil. Accordingly, it is extremely easy to detect the plasma generation location and the concentration (amount) of the plasma. The plasma density distribution can be easily controlled by controlling the position of the coil or by dividing the coil into an inner and an outer coil respectively provided at an inner and an outer peripheral side of the wafer and controlling a voltage applied to each coil. Since the processing gas can be turned into a plasma simply by providing the coil at the ceiling wall of the processing chamber, the plasma process can be carried out cost-effectively.
However, when the coil is installed on the gas shower head formed of a metal which is provided at the ceiling wall of the processing chamber, the electric field is blocked by the gas shower head. Therefore, in order to form the uniform electric field in the processing region, the shower head formed of a metal cannot be used. However, a dielectric material, e.g., quartz, has poor workability compared to a metal, so that it is difficult to form the gas shower head by using the dielectric material in view of workability. For that reason, in case of employing such method, instead of providing the gas shower head, gas injection openings are formed at, e.g., a center portion of the ceiling wall and the sidewall of the processing chamber, and the processing gas is supplied through the gas injection openings. Hence, the uniformity of the distribution of the processing gas is decreased compared to the case of using the gas shower head. Moreover, since the concentration of the processing gas is non-uniform near the ceiling wall or the sidewall of the processing chamber, a large gap needs to be provided between the wafer (mounting table) and the ceiling wall or the sidewall of the processing chamber in order to improve the concentration distribution of the processing gas near the wafer. However, this results in scaling up of the processing chamber. Further, when the ceiling wall of the processing chamber is formed of a dielectric material, e.g., quartz, it is difficult to form a cooling water path at the ceiling wall in view of workability and, hence, it is difficult to control the temperature of the ceiling wall.
The above-described methods have advantages and disadvantageous, so that the use of only one of these methods is not enough to supply the processing gas such that the concentration distribution thereof becomes uniform in accordance with the various processing conditions and to convert the processing gas into a plasma uniformly. Thus, an etching rate, for example, may be varied in the wafer plane. In the method using microwaves as well as in the ICP processing method, it is difficult to control the flow rate of the processing gas or the temperature of the ceiling wall. In order to uniformly supply the processing gas and uniformly convert the processing gas into a plasma, there has been examined a technique for applying an ICP processing method to a CCP plasma processing apparatus by providing a dielectric member around the gas shower head formed at the ceiling wall of the processing chamber and winding a coil on the dielectric member coaxially with respect to the wafer. Besides, there has been examined a method for applying a DC voltage to a gas shower head in a CCP plasma processing apparatus, which is described in Japanese Patent Application Publication No. 2006-286813 (especially, FIG. 1). Although these methods can slightly improve the uniformity of the etching process, a method capable of performing uniform processing is still required.
As the opening diameter of the aforementioned pattern mask is reduced, the in-plane uniformity of the processing needs to be improved. Thus, as miniaturization of wiring structures progresses, more uniform plasma generation is required. When a large wafer having a diameter of, e.g., about 450 mm (18 inches), is used instead of a currently used wafer having a diameter of about 300 mm (12 inches), a large plasma suitable for the large wafer needs to be generated and, hence, a technique for ensuring more uniform plasma generation is required.
The method using microwaves has been known as one of the methods for performing a plasma process by using a plasma of a processing gas. In this method, a processing gas is converted into a plasma in a processing chamber by supplying microwaves from a microwave generating unit to an antenna installed at a ceiling wall of the processing chamber which is formed of a dielectric material, e.g., quartz. Accordingly, a plasma having a low electron temperature, for example, can be obtained.
In this method, since the ceiling wall of the processing chamber is formed of a dielectric material, the gas shower head having a plurality of gas supply holes for supplying the processing gas to the wafer cannot be installed at the ceiling wall of the processing chamber. It is difficult to form the gas shower head by using a dielectric material due to its low workability. Further, when the gas shower head formed of a metal that is easily processable is provided below the antenna, the microwaves are blocked by the gas shower head. To that end, in this apparatus, gas supply holes are formed, e.g., at the central portion of the ceiling wall of the processing chamber, and the processing gas is supplied through the gas supply holes into the processing chamber. However, this may lead to non-uniformity of the concentration distribution of the processing gas in the wafer plane. Specifically, the concentration of the processing gas tends to be high at the central portion of the processing region and low at the peripheral portion of the processing region. In order to reduce the gradient of the concentration of the processing gas near the wafer, a large gap needs to be formed between the ceiling wall of the processing chamber and the wafer. However, this results in scaling up of the processing chamber. Moreover, when the ceiling wall of the processing chamber is formed of a dielectric material, it is difficult to provide a coolant channel for circulating cooling water in the ceiling wall of the processing chamber and, accordingly, the temperature of the ceiling wall is not controllable.
Hence, in order to uniformly supply the processing gas and uniformly convert the processing gas into a plasma by microwaves, there has been examined a method in which a gas supply unit formed of a dielectric material, e.g., quartz, and having at a bottom surface thereof a plurality of gas supply holes is provided at a middle portion of the processing chamber (between the ceiling wall of the processing chamber and the wafer), which is described in, e.g., Japanese Patent Application Publication No. 2008-140998 (especially, FIG. 2 and paragraphs 0027 to 0029). Further, a plurality of openings is formed at the gas supply unit so that the upper portion (ceiling wall side) and the lower portion (wafer side) of the processing chamber can communicate with each other. A gas for plasma generation, e.g., Ar gas, is turned into a plasma by microwaves in the upper portion of the processing chamber, and the plasma thus generated is directed downward to be supplied toward the wafer through the openings of the gas supply unit. Accordingly, the processing gas is turned into a plasma even in the lower portion of the gas supply unit.
Such processing gas supply method enables uniform distribution of the processing gas compared to the method for supplying the processing gas from the central portion of the ceiling wall of the processing chamber. However, in this method, the openings are formed at the gas supply unit, so that the amount of the processing gas is small below the openings, and a plasma is non-uniformly generated. As a consequence, the arrangement pattern of the openings may be transferred to the wafer.
As the opening diameter of the pattern mask is reduced, the in-plane uniformity of the processing is required. Hence, as miniaturization of wiring structures progresses, a plasma needs to be generated more uniformly. When a large wafer having a diameter of, e.g., about 450 mm (18 inches) is used instead of a wafer having a diameter of, e.g., about 300 mm (12 inches), a technique for ensuring more uniform plasma generation is required in order to generate a large plasma suitable for the large wafer. In the large wafer, the uniformity of the plasma process may be deteriorated in the circumferential direction, so that a technique for improving the uniformity of the plasma distribution in the circumferential direction as well as the diametrical direction is required.